Wireless mobile telecommunication systems such as the 3GPP defined UMTS and LTE systems have been designed to provide high data rate mobile communication services to users of communication terminals. Conventionally an LTE network would be expected to provide communication services to communication terminals such as smartphones and personal computers (e.g. laptops, tablets and so on). These types of communication services are typically provided with high performance dedicated data connections optimised for high bandwidth applications such as streaming video data. However, recent developments in the field of machine type communication (MTC) (sometimes referred to as machine to machine (M2M) communication) have resulted in more diverse applications being developed to take advantage of the increasing ubiquity of mobile telecommunication networks. As such it is increasingly likely that an LTE network will also be expected to support communication services for devices such as smart meters and smart sensors. Devices such as these, generally classified as “MTC devices”, are typically less complex than conventional LTE communication terminals such as smartphones and personal computers and are characterised by the transmission and reception of relatively low quantities of data at relatively infrequent intervals.
However, certain aspects of LTE type systems are not optimised for the operation of MTC devices. For example, generally LTE communication terminals exist in one of two logical states: attached or detached. In the detached state, the communication terminal is typically either powered off or de-registered if out of range of the network for a long time. In the attached state the location of the communication terminal is monitored by the network and the device also remains powered up ready to receive paging messages from the network.
This can be inefficient for MTC devices, particularly if they are deployed in large numbers. Firstly a large quantity of network resource would be required to support a high number of devices and secondly, in order for an MTC device to stay in the registered state, it is required to keep its transceiver circuitry powered up to monitor the paging channels. In low complexity devices which may not have access to an external power supply, this power consumption may be undesirable.
Accordingly, efforts have been made to define a new “offline” state specifically for MTC type devices. In the offline state it is intended that MTC devices can still be paged but the amount of network resource that is required to support the offline state is reduced along with the amount of power consumed by the MTC device when in the offline state. However, so far, conventional LTE network architecture does not support the offline state.